As shown in FIGS. 1 and 2, conventional solar heat collecting apparatus for absorbing solar heat energy have been made as described below.
A heat collecting fin 3 attached to a cylindrical inner member 2 is mounted in a cylindrical outer member 1 through which solar heat energy may be penetrated. The cylindrical inner member 2 may absorb solar heat energy and the inside thereof is formed as a passage for a heating medium. Then, the end portions of the inner member 2 are inserted into supports 5 disposed at metallic end plates 4, and the tips of the supports 5 are hermetically sealed to the inner member 2 by silver solder 6. The open ends of the outer member 1 are then joined to the hook-shape peripheries of the end plates 4 by bonding material 7. From an exhaust tubulure 8 disposed at the peripheral surface of the outer member 1, the inside of the outer member 1 is then exhausted and evacuated for efficiently insulating and for preventing the occurrence of dew condensation on the inner surface of the outer member 1.
However, in accordance with such a conventional solar heat collecting apparatus, when joining the open ends of the outer member 1 to the peripheries of the end plates 4, the hook-shape peripheries of the end plates 4 may permit the outflow of the bonding material 7 thereby to secure the quantity of bonding material with difficulty, thus resulting in ineffective workability and increased manufacturing cost.
Furthermore, due to difference in thermal contractility between the outer member 1 and the inner member 2, the end plates 4 are bent and subsequently cracks will take place in the bonding material 7 securely solidified on the surfaces of the end plates 4, thus impairing the airtightness provided in the inside of the outer member 1.
There has been another type solar heat collecting apparatus in which the end plates for hermetically closing the open ends of the cylindrical outer member are provided at the peripheries thereof with annular grooves to be charged with bonding material. However, the conventional apparatus of this kind has been formed such that the outer peripheral walls of the annular grooves are higher than the inner peripheral walls. Accordingly, when the open ends of the outer member are inserted into the annular grooves charged with bonding material, the surplus bonding material flows from the annular grooves toward the center portions of the end plates over the inner peripheral walls of the annular grooves. On the other hand, the end plates have generally been made of metallic material and have had resiliency, but the bonding material used as melted has then solidified and had no resiliency. Accordingly, when the inner member were expanded and contracted by heat or if any shocks were exerted to the end plates during the transportation, the installation or the handling of the solar heat collecting apparatus, the end plates have been deformed. At the time of such deformation, cracks have often easily taken place in the bonding material flowed from the annular grooves toward the centers of the end plates over the annular groove inner peripheral walls, because the bonding material layers were thin. If such cracks have once taken place even though they are small, the cracks have caused the bonding material in the annular grooves also to be cracked whereby the vacuum formed in the outer member is easily broken.
It is an object of the present invention to provide a solar heat collecting apparatus in which an annular groove adapted to be charged with bonding material is formed at the periphery of each of the end plates for hermetically closing the open ends of the cylindrical outer member through which solar heat energy may be penetrated, and the outer peripheral walls of the annular grooves are formed as lower than the inner peripheral walls thereof, so as to prevent the bonding material from flowing from the annular grooves toward the centers of the end plates over the annular groove inner peripheral walls, thereby to prevent the occurrence of cracks in the solidified bonding material and subsequently prevent the break of the vacuum formed in the inside of said outer member, whereby the apparatus may be improved in reliability and life-time.
It is another object of the present invention to provide a solar heat collecting apparatus in which a contractible portion is formed at each of the end plates, so as to absorb the thermal expansion and contraction of the inner member serving as a passage of a heating medium, and to prevent the occurrence of cracks in the solidified bonding material, thereby to subsequently prevent the break of the airtightness provided in the outer member and therefore the rupture of the outer member itself.